This invention relates generally to carburetors and more particularly to carburetors for providing an enriched fuel and air mixture during starting and warming up of an engine.
Some current diaphragm type carburetors utilize engine crankcase pressure pulses applied to the so-called dry side of a carburetor fuel control diaphragm to control or enrich the carburetor fuel and air mixture delivered to an engine during starting and warming up of the engine. Application of engine crankcase pressure pulses in carburetors, as disclosed in U.S. Pat. No. 4,814,114, is controlled by a manually operated, three-position valve. The valve has a fully closed position, a fully open position and an intermediate position between the fully closed and fully open positions.
To start an engine having this type of carburetor, the air is purged from the carburetor, such as by manually depressing an air purge bulb, the throttle valve is moved to its starting position and a three position valve is moved to its fully open position permitting engine crankcase pressure pulses to act on the fuel control diaphragm. The operator then tries to manually start the engine such as by pulling an engine starter rope or cord until engine combustion is initiated but not normally sustained and the engine stalls or dies rich. The valve is now manually moved to its intermediate position decreasing application of engine crankcase pressure pulses to the fuel control diaphragm. The operator then tries to restart the engine manually until the engine is started and operation of the engine is sustained. After a short period of time sufficient to allow the engine to warm up, the valve is manually turned to its fully closed position preventing the application of engine crankcase pressure pulses to the fuel control diaphragm.
Starting an engine having a carburetor with this manual three position choke valve can be difficult for unskilled operators who are unfamiliar with the multi-step engine starting process required with this type of carburetor. Further, the starting procedure has to be modified under different temperature conditions and the operator must have the knowledge and skill to employ the necessary modified starting procedure.
A carburetor having two paths each with a valve for application of pressure pulses to a fuel metering assembly of the carburetor to provide an enriched fuel and air mixture to the engine to facilitate starting the engine and warming it up. Preferably, the pressure pulses are obtained from a crankcase chamber of the engine. A first valve in one path is preferably actuated by a diaphragm controlled automatically by a pressure signal from a carburetor fuel pump so that at low fuel pressure, such as during manual pulling of the engine starter rope, the first valve is open and at higher fuel pump pressure, such as when the engine is initially started and thereafter during engine operation, the first valve is closed. A second valve in the second path may be manually actuated to an open position to facilitate starting and warming up of the engine and closed after the engine is warmed up, to prevent the application of the crankcase pulses on the fuel metering assembly. Preferably, the second valve is actuated to close with manual opening of a throttle valve of the carburetor. Both of the first and second valves control the application of crankcase pressure pulses to the fuel metering assembly to cause the fuel metering assembly to deliver a fuel and air mixture which is richer than required for normal operation of the engine.
Desirably, with both valves opened, maximum fuel enrichment is obtained and with only one of the valves opened a lesser fuel enrichment is obtained. Accordingly both valves are preferably opened to facilitate starting the engine with a maximum enrichment of the fuel and air mixture during cranking, and after starting, one of the valves is preferably closed to reduce the enrichment while the engine warms up. Thereafter, the remaining open, valve is closed so that the fuel metering assembly operates in its normal fashion to provide the desired fuel and air mixture to the engine during its normal operation.
Objects, features and advantages of this invention include providing a carburetor which provides an enriched fuel and air mixture to an engine to facilitate starting the engine, provides an enriched fuel and air mixture to facilitate warming up the engine, enables varying fuel enrichment at starting and warming up of the engine, greatly facilitates starting the engine, eliminates the need for a three position butterfly-type choke valve, provides a reduced enrichment during warming up of the engine to eliminate stalling, provides a quick and automatic switch from maximum enrichment to a lesser enrichment to prevent stalling of the engine after initial cranking and starting of the engine, is of relatively simple design and economical manufacture and assembly and in service has a long useful life.